Therapy involving the adminstration of intravenous solutions to patients is in wide-spread use. The solution may be administered continuously over a long period of time, as for example a glucose solution or an antibiotic in solution; or may be administered periodically (say every 4, 6 or 8 hours), as for example in the case of certain antibiotics. In either of these situations it is necessary for the vein to remain accessible and patent (that is, open) without the necessity of multiple venous punctures. It is common practice to insert into the patient's vein a needle having a hub and an adapter, commonly known as a heparin lock, thereon. The heparin lock is simply a piece of self-sealing rubber or other elastomer removably attached to the hub of the needle. To prevent blood clotting in the needle, i.e. to maintain patency, saline and heparin solutions must be injected in that order into the needle from separate syringes, approximately once every 6 to 8 hours. Typically these solutions are injected through the heparin lock.
It is established medical practice to confirm proper placement of the needle into the patient's vein, to flush the needle, and to maintain patency. To confirm proper placement, one inserts the needle of a saline-filled syringe through the heparin lock into the needle and raises the plunger of the syringe so as to withdraw a small amount of blood from the patient's vein into the syringe. This is commonly known as a blood return. Thereafter, to flush the needle, saline solution is injected from the syringe through the needle into the patient. Finally, to maintain patency, it is necessary to inject heparin periodically, say once every 6 to 8 hours. This, of course, requires a second syringe, one which has been filled with a heparin solution.
A typical procedure for injecting the saline and heparin solution into a patient is as follows: Step one, the person administering the injection first withdraws the saline solution from a vial into the syringe. Step two, the person injects this solution into the patient. Step three, the person takes a second syringe and needle and withdraws the heparin solution from a vial. Step four, the person injects this solution into the patient.
This procedure is typical of the procedure that would be followed for injection of any two liquids in predetermined sequence into a patient.
It will be appreciated that there are chances for error, both in measuring the amount of each ingredient to be administered and in administering the substances in the correct sequence. For example, in administering heparin, the saline solution is always administered first, followed by the heparin solution.
Because of the several steps required and the use of multiple dose vials for saline, there is a possibility of contamination. There is also a possibility of medication error.
Saline and heparin solutions have recently become commercially available in cartridge form. Each cartridge contains the required dosage. Although this eliminates the possibility for dosage error, the possibility of incorrect order of insertion remains. To use cartridges of saline and heparin solutions (each of which includes its own needle), it is necessary to insert each of the cartridges in turn into a cartridge holder (which includes a plunger), the saline cartridge being inserted first, and to follow the same four steps which have been previously given for injecting the saline and heparin solutions into the patient.
In certain other situations two liquids must be injected into a patient either mixed or separately in either order. One such situation is simultaneous administration of two different types of insulin (regular normal and long acting, for example), to a diabetic patient. Insulin injection is complicated by the fact that dosage requirements vary from patient to patient and even for the same patient. One procedure presently used is as follows: the person administering the insulin injects into the first multiple dose vial (Vial No. 1), which contains one kind of insulin, a volume of air equal to the amount of insulin to be withdrawn from that vial. Then he/she withdraws the required amount of insulin from Vial No. 1 into the syringe. Then, after removing the needle from Vial No. 1, the person further withdraws the plunger to fill the syringe with the proper amount of air for injection into Vial No. 2, which contains a second type of insulin. The person inserts the syringe into Vial No. 2 and carefully expel the air in the syringe into Vial No. 2 taking care not to expel any solution of the syringe into Vial No. 2. Then the person withdraws the plunger, which causes the solution from Vial No. 2 to be drawn into the syringe. The syringe is then ready for injection. As one can appreciate, it is very difficult to expel the required amount of air into Vial No. 2 without also expelling a small amount of insulin from Vial No. 1. If some insulin from Vial No. 1 is expelled, of course some insulin from Vial No. 1 will be introduced into multiple dose Vial No. 2, so that Vial No. 2 no longer contains a pure solution of insulin of the second type.